Abstract

The discovery [1] of high temperature oxide superconductors has caused tremendous excitement due to great technological importance. The critical current in polycrystalline oxide superconductors is low. Cava et al. [2] first measured critical current density, Jc in Y1Ba2Cu3O7 by transport method and reported Jc at 77K and zero magnetic field to be only 1100 A/cm2, compared to 105 A/cm2 reported [3] for epitaxial films. Moreover, the critical current in the polycrystalline material decreases drastically [4] at a low magnetic field. Similar low critical currents have also been observed [5] in polycrystalline Bi2CaSr2Cu2O8 and T12Ca2Ba2Cu3O10 compounds. Weak linking at the grain boundaries is thought [6] to be the cause for low Jc in polycrystalline high-Tc materials. By measuring Jc across single grain boundaries between [001] oriented grains of Y1Ba2Cu3O7, Mannhart et al. [7] have shown that high angle tilt grain boundaries behave like normal layers in SNS-type Josephson junctions.